Researchers have found evidence of large predatory worms — some as long as 6.5 feet (2 meters) — that roamed the ocean floor near Taiwan over 20 million years ago. The finding is the result of reconstructing an unusual trace fossil that they identified as a burrow of these ancient worms.
Geologists discovered the peculiar giant L-shaped trace fossil – a geological feature, like track marks or a burrow – in a 20-million-year old layer of rock on the northeast coast of Taiwan. In a three-year investigation, an international research team reconstructed the unusual fossil and reached the conclusion that the trace fossil was the burrow of an extinct predatory worm that would surface from the ocean floor to grab prey and drag it into its lair.
I was fascinated by this monster burrow at first glance. Compared to other trace fossils which are usually only a few tens of centimeters long, this one was huge – 2 meters long and 2-3 centimeters in diameter. The distinctive, featherlike structures around the upper burrow were also unique and no previously studied trace fossil has shown similar features.
The researchers say the ancient worm was similar to the modern-day Bobbit worm, which is also large and predatory, and is sometimes called the “sand striker,” sensing prey with its antennae, then grabbing them with its powerful jaws, and retreating into its burrow. The study authors wrote:
We hypothesize that about 20 million years ago, at the southeastern border of the Eurasian continent, ancient Bobbit worms colonized the seafloor waiting in ambush for a passing meal … When prey came close to a worm, it exploded out from its burrow, grabbing and dragging the prey down into the sediment. Beneath the seafloor, the desperate prey floundered to escape, leading to further disturbance of the sediment around the burrow opening
Further analysis revealed a high concentration of iron around the upper burrow, leading researchers to believe the worm secreted mucus to reinforce and rebuild its burrow wall after each feeding.
Marine predatory worms have existed for more than 400 million years, since the early Paleozoic era, but their soft tissue bodies decay leaving little trace of their existence behind. This trace fossil is believed to be the first known produced by a sub-surface ambush predator, allowing researchers a rare opportunity to learn more about this ancient sand striker’s behavior.
Bottom line: On the northeast coast of Taiwan, geologists discovered a peculiar giant L-shaped burrow in a 20-million-year old layer of rock. An international research team concluded that the burrow was the home of a giant, predatory sand worm.
Eleanor Imster has helped write and edit EarthSky since 1995. She was an integral part of the award-winning EarthSky radio series almost since it began until it ended in 2013. Today, as an EarthSky.org Editor, she helps present the science and nature stories and photos you enjoy. She and her husband live in Tennessee, where they enjoy guitar playing and singing. They have 2 grown sons.